DC-DC converters are used in difference applications, particularly consumer electronics, such as notebook, desktop, personal digital assistant (PDA) and so on. The DC-DC converters need to be able to provide a stable power supply to electronic device at a preset and stable voltage.
Constant ON-time DC/DC converters are widely used due to their excellent load transient response, high efficiency, simple configuration and small size. FIG. 1 schematically illustrates a traditional DC/DC converter 100 with constant ON-time control. When an output voltage Vout of the converter is lower than a preset voltage, the converter is configured to provide power from an input terminal to an output terminal. As one example shown in FIG. 1, output voltage Vout is sensed via a voltage divider comprising a resistor 106 and a resistor 107, the common node of resistor 106 and resistor 107 is configured to provide a feedback signal FB. Feedback signal FB is coupled to a comparator 108 and is compared with a reference signal Vref which is constant and predetermined. When feedback signal FB is less than reference signal Vref, a driving circuit 109 coupled to an output of comparator 108 is configured to provide an activating drive signal PWM1 to turn ON a high-side switch 101, then a current is supplied from the input terminal to the output terminal. An ON-time count circuit 110 coupled to driving circuit 109 is employed to provide a preset constant ON-time period TON for high-side switch 101, and high-side switch 101 is turned OFF after ON-time period TON expired.
FIG. 2 schematically illustrates a dual-phase DC/DC converter 200. As shown in FIG. 2, dual-phase DC/DC converter 200 comprises a first phase circuit and a second phase circuit. The first phase circuit comprises switch 101, a switch 102 and an inductor 103, and the second phase circuit comprises a switch 201, a switch 202 and an inductor 203. ON-time count circuit 110 and driving circuit 109 are employed to supply drive signal PWM1 to switch 101, and an ON-time count circuit 210 and a driving circuit 209 are employed to supply a drive signal PWM2 to switch 201. The same as converter 100, when feedback signal FB is less than reference signal Vref, comparator 108 is configured to provide an activating signal SET (e.g., signal SET is logic HIGH), and activating signal SET is distributed to driving circuit 109 and driving circuit 209 alternately via a frequency divider 211 as shown in FIG. 4. When signal SET is activated, drive signal PWM1 and drive signal PWM2 are set activated alternately, switch 101 and switch 201 is then turned ON alternately. When switch 101 is turned ON, ON-time count circuit 110 starts to count, and switch 101 is turned OFF until ON-time period TON has expired. When switch 201 is turned ON, ON-time count circuit 210 starts to count, and switch 201 is turned OFF until ON-time period TON has expired.
FIG. 3 schematically illustrates a multiphase DC/DC converter 300 comprising N phase circuits, wherein N is an integer and larger than 1. Similar with converter 200, activating signal SET is distributed to each phase circuit alternately via a frequency divider 311. When signal SET is activated, switches of each phase circuit are turned ON alternately, an ON-time count circuit corresponding to an activated phase circuit starts to count, and each switch is turned OFF until ON-time period TON has expired.
FIG. 4 shows waveforms illustrating signals of converter 200. For multiphase converter, when parameters, e.g., inductance, resistance, ON-time period and so on, of different phase circuits are the same as each other, phase shift of each phase circuit is generated automatically and phase interleaving may be symmetry. But as FIG. 4 shown, phase interleaving is not perfect, i.e., for dual-phase converter, phase shift between the phase circuits is not 180 degree, per any parameter of different phase circuits is different. As a result, different phase circuits may under different electrical stress.
Thus, a multiphase converter with controllable phase shift is needed to achieve phase symmetry even with different parameters.